The survey found that teenagers were, more than ever, having their lives exposed through online communication. Photograph: Alamy

The self-esteem of teenage girls has fallen significantly since the start of the economic downturn seven years ago and the boom in the use of social media and online communication, a major survey of 30,000 school pupils has revealed.

Analysts who compile the survey for schools across the country have reported a worrying drop in the number of 14- and 15-year-olds, particularly girls, who say they feel highly confident in their own worth.

After consistent year-on-year increases since the early 1990s in the number of young people scoring in the highest bracket of self-esteem, a sudden and dramatic change occurred after 2007, according to the Schools Health Education Unit, which works with local authorities to monitor the health and lifestyles of pupils.

From a peak in 2007, when 41% of 14- and 15-year-old girls reported high self-esteem, that figure has fallen to 33%. There has also been a less significant drop in self-esteem among boys of the same age, from 55% in the highest bracket in 2007 to 50% in 2013, according to the survey, released on Sunday.

Dr David Regis, research manager at the unit, said that the correlation with the economic downturn could not be ignored and that more attention might need to be paid to the sensitivities of young people to their families’ plight during the recession and slow recovery.

The unit also suggested that teenagers were, more than ever, having their lives exposed through online communication and that schools should examine whether they were educating their pupils properly on the dangers.

Three in four 14- and 15-year-old girls have chatted on the internet and 13% have received a message that scared or upset them. One in five had chatted with people they did not know. A third of all pupils (34%) in one authority had looked online for pornographic or violent images, films or games.

Regis said: “We have always been concerned about the emotional wellbeing of young people. A while ago we took stock of young people’s emotional wellbeing as seen in our figures. At the time, we were fairly sanguine, as we thought that, while different worries came and went, young people’s self-esteem was holding up well and even increasing.

“But it is no longer the case: the data series shows a peak in the percentage of year 10 females [aged 14-15] scoring in the highest bracket of self-esteem scores in 2007, but the figures in that group have since declined.”

Angela Balding, who managed the survey for the unit, which has carried out the polling since 1976, said: “The 2008 date coincides with the economic recession, so that’s a plausible explanation of what we see – but we are also aware of new pressures about being online and of online bullying.

“We can also see among the pupils with low self-esteem that they are much more likely than their peers to have experienced bullying at or near school in the last year. We don’t know if that’s because bullying causes a drop in self-esteem, or if pupils with low self-esteem are more likely to be picked on, or both.”

A third of girls (31%) aged 10 or 11 fear bullying at least sometimes. One in five girls of that age said their school did not deal with bullying very well. Ellie Dibben, 18, from Hertfordshire, who is a member of the 18-strong “advocates”, a panel of the charity Girlguiding, which examines issues pertinent to young women, said she recognised the downturn in self-esteem among her peers.

She said: “I think that recently we have had a very fast period of change in terms of online habits. But while we have had these huge changes come in, we have not had changes in the way we are educated in an era of an increasingly sexualised media. Some young people have no idea how to deal with this.”

The survey also reveals a worrying attitude among teenage girls to eating. It found that 14% of 14- and 15-year-old girls have nothing to eat or drink for breakfast, with 13% having only a drink. Nearly two in three (62%) of girls of the same age and 53% of year 12- and 13-year-olds would like to lose weight.

However, there is good news in terms of the attitudes of teenagers towards alcohol and tobacco. Since the mid-1990s there has been a general decline in the percentage of 14-15-year-olds who smoke regularly, the survey found. For example, in 1985, 33% of 14-15-year old girls said they had never smoked. In 2013, this had risen to 60%.

About 97% of 10-11-year-olds say they have never smoked. This figure drops to 66% (boys) and 60% (girls) by the time they are 14-15 years old. More than a third (35%) of 12-15-year-olds live in a home where someone smokes. One in five (22%) of 14-15-year-old girls reported smoking and 27% reported drinking alcohol “in the last seven days”.